Quoted from:Estimation of Global Solar Radiation on Horizontal Surfaces Over Egypt[J]. Egyptian Journal of Solids, 2005.https://doi.org/10.1016/j.enpol.2009.04.038
INTRODUCTION
The measured data of the monthly average global solar radiation on a horizontal surface H and the number of bright sunshine hours n for five locations in Egypt are analyzed. The selected locations represent the various weather conditions of Egypt. Matruh, Rafah and Al-Arish are in the north, Tanta in the middle and Aswan in the south. The regression constants for the first, second and third order Angstrom type correlations for each location have been calculated using the method of regression analysis. Comparisons between measured and calculated values of H are performed for the present locations. The values obtained for the RMSE, MBE and the MPE indicated that the second and third order Angstrom type correlations do not improve the accuracy of estimation of global radiation. Therefore, the measured data available for the selected locations are combined and a first order correlation has been proposed for all Egypt. Moreover, all Egypt correlation is extended to other Egyptian locations which are not included in the regression analysis. Comparisons between measured and calculated global radiation indicated that all Egypt correlation is applicable for any location of Egypt and may be extended outside Egypt for places which have the same values of the maximum clearness index (a + b).
The objective of the present study is to present and analyze the global solar radiation and sunshine duration data recorded at five cities (Matruh, Rafah, Al-Arish, Tanta and Aswan) in Egypt, and to develop new constants for the first, second and third order Angström type correlations which may be usedfor estimating H at any location of Egypt. Performance of the new constants is checked by comparing the estimated and measured values of global solar radiation. Statistical comparisons between measured and estimated global solar radiation indicated that the second and third order Angström type correlations do not improve the accuracy of estimation of global solar radiation. Therefore, first order or linear correlations between the monthly average daily clearness index H / Ho and the relative possible sunshine duration n / N for the selected locations and also for all Egypt have been proposed. All Egypt correlation is then extended to other four Egyptian locations not included in the regression analysis. It is concluded that the correlation proposed for all Egypt can be used successfully for estimation of H for any location of Egypt with a reasonable accuracy and may be extended outside Egypt for locations of similar meteorological characteristics.
El-Sabaii and Trabea reported the following first-order Angstrom-type correlations for Egypt using the measured data for five Egyptian locations (Al-Arish, Rafah, Matruh, Tanta, and Aswan):
\( 𝐻/𝐻_0 = 0.3647 + 0.3505 𝑆/𝑆_0 . \)
CONCLUSIONS:
On the basis of the obtained results for five locations in Egypt, the following conclusions may be drawn: (i) The second and third order Angström type correlations do not significantly improve the accuracy of estimation of the monthly average daily global radiation incident on a horizontal surface H.Therefore, a first order correlation is proposed for each location. (ii) The proposed first order correlations are able to predict the global radiation with percentage error for a single month never exceeds ± 10% in any of the locations. (iii) The proposed correlation for all Egypt, Equation can be used for estimating H for any location of Egypt with absolute values of the MPE less than 6%. All Egypt correlation may be extended outside Egypt for places which have the same values of the maximum clearness index.